This invention relates to a method of plugging the open end of an intramedullary bone canal with an inflatable device which is capable of restricting the flow of bone cement, particularly during the pressurized injection of bone cement, during a procedure involving the implantation of a joint prosthesis to the end of a bone. The device is further capable of deflating in a relatively short period of time after the cement hardens to avoid possible weakening of the cortical bone surrounding the inflated device. This invention also relates to the inflatable bone cement restrictor device ("inflatable bone plug") used in such a method.
Degenerative bone diseases and injuries to the joints often make it necessary or desirable to replace the natural joint with an artificial prosthesis One such replacement involves the fixation of an artificial hip joint prosthesis to the proximal end of the femur. The femur contains a hollow intramedullary bone canal running through its central long axis. It is desirable to affix a hip joint prosthesis to the femur in such a manner that the stem of the prosthesis lies along the central long axis of the femur. In preparing the proximal end of the femur to receive such a prosthesis, an appropriately sized opening to receive the stem of the prosthesis is made in the proximal end of the femur. That opening normally extends into the intramedullary bone canal approximately along the central long axis of the femur and is wide enough to permit bone cement to be compacted about the stem to secure the prosthesis to the femur.
To prevent bone cement from flowing deeper into the intramedullary bone canal than is necessary, an intramedullary bone canal plug ("bone plug") composed of a piece of the removed femur or a plug of partially cured bone cement has been used to restrict the flow of cement. Likewise various bone plugs having sides which press-fit against the cortical bone forming the canal to form a seal have been proposed in U.S. Pat. Nos. 4,245,359 (Stuhmer, issued Jan. 20, 1981); 4,302,855 (Swanson, issued Dec. 1, 1981) and 4,293,962 (Fuson, issued Oct. 13, 1981). Press-fit bone plugs are generally designed to be inserted in one direction and have the disadvantage of not always being removable once they are inserted. This can be a disadvantage where the plug has inadvertently been inserted too deeply into the intramedullary bone canal. Another disadvantage of such a plug is evidenced when too large of a size has been selected and the plug can neither be inserted to the proper depth without the use of excessive force nor can it be easily removed.
Since the femur is composed of living tissue which is permeated with blood vessels and tissue fluid, the escape of blood and tissue fluid can result in poor adherence of the bone cement to the femur. For this reason, it has become more common to inject cement into the opening in the proximal femur under pressure to cause the bone cement to permeate into the porous bone structure and thereby obtain better adhesion to the femur. See, for example, U.S. Pat. Nos. 3,889,665 (Ling, et al., issued June 17, 1975), 4,357,716 (Brown, issued Nov. 9, 1982) and 4,462,394 (Jacobs, issued 7/31/84) for examples of such pressurized bone cement injection processes. Press-fit bone plugs have a further disadvantage when used in pressurized injection systems because the pressure can drive the plug down the canal much further than is necessary or desirable.
Use of a very tightly fitting press-fit plug to avoid plug movement has further disadvantages such as causing a change in the flexural rigidity of the cement/bone system as discussed in U.S. Pat. No. 4,344,190 (Lee, et al., issued Aug. 17, 1982). The Lee, et al. Patent notes that change in the flexural rigidity of the cement/bone system can increase the risk of bone fracture at the point where the plug presses against the bone. Lee, et al. state that a fracture at that point is very difficult to set. If a press-fit plug is too large for the intramedullary bone canal opening, a surgeon may not, or may only with great difficulty, be able to remove the plug once it is inserted in the opening. The answer provided by Lee, et al. is to construct a press-fit bone plug of a biodegradable material which is reabsorbed by the body after the cement hardens. The pressure against the bone is thereby relieved by reabsorption after the cement hardens and the risk of a fracture occurring in that area is said to be reduced. No mention is made as to the length of time required before a sufficient level of resorption of the plug occurs to release the pressure. Furthermore, there is no way to adjust to tightness of fit other than by plug size selection. Once inserted, the plug appears to be difficult to remove and, once inserted, a less than optimally-fitting plug could be driven deeper into the canal by the pressure of the cement being injected.
One bone plug designed to be securely fastened inside of the intramedullary bone canal is taught in U.S. Pat. No. 4,447,915 (Weber, issued May 15, 1984). The Weber Patent teaches a two piece medullary bone canal plug formed by a deformable and expandable outer body having a jacket formed of a number of segments and a conical expansion body which is pulled into the outer body to expand the outer body. Once pulled together, the two bodies are permanently secured together via serrations of the inside of the outer body and the outside of the expansion body. However, it appears that once the two bodies are secured together, the plug cannot be removed if for some reason that should become desirable. Likewise, if the plug is secured so that too much pressure is exerted against the sides of the intramedullary bone canal, the presence of the plug may increase the risk of fracture as noted in the Lee, et al. patent above.
There appears to be a need for a bone plug which possesses the following characteristics: (a) it should be capable of being used for a variety of intramedullary bone canal or operative opening sizes in a bone for reception of a joint prosthesis; (b) it should be capable of being tightly secured to a controllable degree against the walls of the canal or opening to restrict the passage of bone cement, particularly cement injected under pressure, past the plug even when the bone plug is placed beyond the isthmus of a bone such as in the femur, (c) it should be capable of being removed after securement against the wall prior to the placement of bone cement into the intramedullary bone canal or opening and (d) it should be capable of releasing the pressure against the wall of the canal or opening in a relatively short period of time after the hardening of the bone cement to decrease the risk of bone resorption and remodelling or changes which could result in fracture of the bone due to stresses on the walls of the canal or opening surrounding the plug. The object of this invention is to provide a bone plug possessing such characteristics and a method for using the same to accomplish the fixation of an artificial joint prosthesis on the end of a bone. In accordance with this invention, this is accomplished through the use of an inflatable bone plug of a biocompatible elastomeric material which is capable of being inflated with a biocompatible fluid to apply a preselected amount of pressure against the walls of the operative opening or intramedullary bone canal and thereby fit tightly into a variety of opening or bone canal diameters. The inflatable bone plug is provided with a means whereby the biocompatible fluid, preferably carbon dioxide gas, used to inflate the plug is retained within the bone plug for a sufficient length of time to prevent the liquid bone cement from passing around the plug and to permit the bone cement to harden. Thereafter, the fluid escapes through a controlled release means from the bone plug and the pressure exerted by the bone plug against the walls is reduced to a minimum.
Miniature detachable balloon catheters which have been used to accomplish the blockage of blood vessels are known and some of these are described in U.S. Pat. Nos. 3,834,394 (Hunter, et al, issued Sept. 10, 1974); 4,311,146 (Wonder, issued Jan. 19, 1982); 4,327,734 (White, issued May 4, 1982); 4,341,218 (U, issued July 27, 1982) and 4,364,392 (Strother, et al., issued Dec. 21, 1982). These devices employ a tiny balloon fixed by means of a valve to the end of a long catheter which is passed as a unit through a blood vessel. The balloon is inflated to accomplish blockage of the blood vessel and the catheter is detached. None of these patents suggest plugging the intramedullary bone canal of a bone with such a device. Furthermore, the balloons described therein are generally not intended to deflate by themselves since it would be undesirable to have the balloon released within a vessel as discussed in the White and the Strother, et al. patents. U.S. Pat. No. 4,213,461 (Pevsner, issued July 22, 1980) describes a miniature balloon catheter which has a pin-hole located opposite the cannula to enable a fluid to be dispersed from the site of the pin-hole for diagnostic purposes. The Ling, et al. Patent describes a pressurized cement delivery system which is used to accomplish pressurized cement delivery with an expandable rubber plug, but the plug is not left in the canal to restrict the flow of cement further into the canal after the stem is inserted, but is designed to seal the open end of the femur from outward escape of cement during pressurization. None of these patents suggest the novel method and device which forms the subject matter of this invention.